Gauge for airfoils



June 25, 1946. H. L. MILNER GAUGES FOR AIRFOILS 2 r S a w 2 @F Patented June 25, 1946 GAUGE FOR AIRFOILS Harry Lawley Milner, Cheltenham, England, assignor to Rotol Limited, a British company Application October 31, 1942, Serial No. 464,087 In Great Britain November 5, 1941 8 Claims; 1

This invention has for its object to provide a new form of gauge or measuring device for use with airfoils, airscrew blades and the like for the determination of the direction of the zero-lift line thereof.

The zero-lift line of a given airfoil section can be obtained with sufficient accuracy for carrying out the method described in my co-pending British application No. 14,282/41 by drawing a straight line through the centre of curvature of thetrailing edge of the section and the point at the mean height of the ordinate at 50% chord. Since in practice it is impossible to draw this line, the present invention provides a gauge which determines the direction of the line and facilitates the measurement of its angular relation with respect to any particular datum direction.

According to this invention, a gauge for determining the direction of the zero-lift line of an airfoil section comprises an abutment to engage and be located by the trailing edge of the section, Jaws so mounted and interconnected as to embrace the airfoil section and move by equal and opposite amounts to and from a datum-lineassociated with the location-point on said abutment and means for adjusting the lengthwise spacing of the jaws along said datum-line from the location-point on said abutment.

According to another feature of this invention, the device comprises a base member having a straight datum-line on it, an abutment mounted .to slide parallel with the datum-line and having a notch on its front face to engage the trailing edge of an airfoil or a blade, a pair of similar rods pivoted on the abutment symmetrically about the notch therein, a second pair of links pivoted on the base at a point on the line of movement of the said notch, said links being pivoted respectively to the ends of the said rods, and pads ad iustable lengthwise on said rods for engaging the front and rear faces of the blade. I 1

In a modified construction according to this invention, it comprises a frame carrying an abutment to engage and locate the trailing edg of the airfoil section, a pair of arms pivoted on said frame symmetrically about said'abutment, means for moving said arms simultaneously and equally towards and away from a line intersecting the location-point on said abutment, pads carried on said arms to engage the front and rear faces of the airfoil section, and adjustable along said arms, and means on said frame for indicating the direction of the said line about whichthe arms move. v 1 I The invention also includes certain specific de-.

tails of the construction as hereinafter set forth.

In the accompanying drawings:

Figure 1 is a more or less diagrammatic view, partly in section, showing the construction and operation of a gauge in accordance with this invention, and

Figure 2 is a similar view of a modified construction of gauge.

Referring first to Figure 1, the device comprises a base or frame-member I0 formed with a flat surface H which as shown, constitutes the bottom of the frame. At each end the frame is provided with upstanding portions I2, l3 respectively, and on the projection l2 there is formed a bore or guide-channel l4 whereof the axis is preferably accurately parallel With the surface I l of the base (if .it is not the lack of parallelism must be computed and taken into account) within this bore there is mounted a stem l5 which is slotted longitudinally at I6 to receive a nut-member l1 which is held against movement in the channel 14. A screw-threaded spindle I8 engages the nut-member I1, and has secured on it a suitable thrust washer l9 engaging the stem IS, with a cover-plate 2D engaging the other side of the thrust washer; this construction provides that rotation of the spindle I8 in the nut-member l1 feeds the stem [5 in one direction or other lengthwise through the channel i4.

On the end of the stem l5 there is mounted a block or abutment 2! formed with a V-notch 22 on its forward face of .a suitable size to receive and locate the trailing edge 23 of an airfoil or blade-section 24. Upon the block 2! there are pivotally mounted two similar rods 25, 26 with their pivotal axes symmetrically disposed with respect to the notch 22. These rods 25, 26 are of equal lengths and their ends are connected respectively to links 21, 28, which links are pivoted on the projection l3 aforesaid of the frame H1. The pivotal connections 29, 30 of these links 21, 28 are disposed symmetrically about the line 3|, which intersects the apex of the V-notch 22, and also constitutes the axis of the channel M.

l Upon each of the rods 25, 26 there is slidably mounted a pad 32, 33 respectively, and these pads can be adjusted to any desired distance lengthwise of the rods from the notch 22 and secured in such setting. To facilitate their adjustment, datum stops 34, 35 are provided on the rods from which the spacing of the pads can be readily measured.

.Itwill be seen that this device provides a duplex toggle linkage which issymmetrical about the line 3|, and that the rods 25, 26 can be rid-- justed simultaneously and equally towards or away from the line 3| by turning the spindle l8 to move the stem longitudinally. When the pads 32, 33 are spaced at equal distances from their respective datum stops 34, 35 they will always be equidistant from the line 3| whatever be the angular separation of the links 25 and 26.

In using this gauge on an airscrew-blade it is threaded on to the blade as illustrated so that the latter lies between the two rods 25, 25 with its trailing edge in the notch 22. and 33 are adjusted on their rods so that each of them is spaced away from the notch 22 by the same amount and at such a distance that pad 33 contacts the section at th foot of the ordinate at 50% chord. The spindle I8 is'turned until the pads 32, 33 are brought int contact with the front and rear faces of the blade respectively. When the blade is thus engaged at the three points 22, 32 and 35, the line 25 passes through the centre of curvature of the trailing edge, and the mean height of the ordinate at 50% chord as above mentioned. Since the base 22 is parallel with this line, it provides a convenient means by which the direction of the line 3| with respect to any convenient datum can be measured. If desired, the whole gauge can be turned upside-down so that the fiat face I is uppermost to receive any desired device by which the angular measurement can be obtained.

In the alternative construction illustrated in Figure 2, the toggle linkage is replaced by asingle pair of arms. The frame of the gauge 36 has the aboutment 37 secured on it'b'y the screw 38, and a V-notch 39 is provided in the abutment to receive the trailing edge of the blade. Two arms 40, 4| are pivoted at 42, 43 respectively on the frame 36 symmetrically on each side of the centre line M of. the V-notch, and are provided with rollers 45,55 toengage fiat surfaces 4'1," 48 respectively on a cross-head 49. This cross-head is mounted to slide along the line, conveniently by means of a tubular guide 58 engaging the stem which carries the abutment 31. It also slides in a bore 52 on the frame 35. The stem 5| is screwthreaded at 53 to receive a nut-member 54 which is engaged with the sleeve 50 to move it and the cross-head in either direction. When moved towards the left in the drawing, the faces '41, 48 on the cross-head engage the rollers 45 and it respectively, and swing the'armslll', 4| towards one another. Each arm is provided with aneXtension-piece 55, 55 respectively, each carrying a pin engaging a slot in the cross-head 49, so that when the cross-head is withdrawn towards the right, the arms 40, 4| are moved apart.

On each of the arms there is provided acontact block 5?, 58, respectively, which may be provided with rollers to engage the opposite faces of the blade, and the blocks are adjustable lengthwise of the arm from datum stops 59, 60 as in the previous construction.

Theframe 56 is formed with a surface 6| which in the present instance is shown at the top of the frame, and which is made accurately parallel with the line 4 1 about which the arms v 4| swing.

The operation of this form of gauge is exactly similar to that described withreference to Figure 1 and need not be repeated.

The zero-lift of an airfoil, as determined by the gauge above-described, may only approximately represent the true zero-lift line, but when the gauge is used for the determination only of errors in the direction of this line, as compared The Dads 4 with another blade or a master blade, the errors involved by the approximation will tend to cancel out. The gauge is found to be satisfactor for use in connection with the invention described in the specification of my concurrent British patent application No, 1%,282/41.

A gauge according to this invention is of especial value when used in connection with airscrew blades made of compressed wood and other materials which in the proces of manufacture become subject to slight deviation in dimensions and shape. When, for example, one face of a blade which is intended to be flat and to be used as a datum-line for measuring the pitch of the blade, is slightly convex at some point, such direct measurements become quite unreliable, and the gauge, by its avoidance of any reference to the fiat face as such, obviates this difficulty, and takes full account of the actual thickness of the blade including any possible convexit or concavity of the flat face.

Whilst particular constructions of gauge comprising toggle-like linkages have been described above, it will be appreciated that various. other mechanical arrangements for applying the jaws or pads to the front and rear surfaces of the blade, at points having a definite relationship to the trailing edge thereof, may be used. Thus, for exampleginstead of controlling the pad-carrying rods by means of links connected to their ends, the rods might be geared together at their axes to move equally and oppositely, or they might be controlled'by engagement of their free ends with a rightand left-handed screw, or they might be angularly adjusted by a wedging device movable along the datum-line through the notch on the abutment; other simple mechanisms for producing equal and opposite movement of the rods will be apparent to those skilled in the art.

I" claim:

1. A gauge for determining the direction of. the zero-lift line of an airfoil section, comprising a base-member having av straight datum-line on it, an abutment mounted to slide, parallel with the datum-line and having "a V-notch on its front face to engage the trailing edge of the blade, a pair of similar rods pivoted on the abutment symmetrically about the notch therein, a pair of links pivoted on the base symmetrically to the line of movement of the said notch, said links being pivotedrespectively to the ends ofthe said rods, and pads adjustable lengthwise on said rods for engaging the, front and rear faces of a blade.

2. A gauge according, to claim 1. including datum stops on said rods.

3. A gauge according to claim 1 including means for adjusting said abutment parallel with said datum line.

4. A gauge for determining the direction of the zero-lift line of an airfoil section with respect to the profile thereof, comprising. a body having two adjustable contact members for engaging the'section on opposite sides thereof, a'third contact member for engagingv the trailing edge ofthe section, and a surface on said body which bears a fixed angular relationship. with, a, line joining said third contact to a point midway between said two contact members, when said members engage said section at appropriate points'on the surfaces thereof. I

5. A gauge for determining the direction of the zero-lift line of an airfoil section with respect to the profile thereof, comprisinga pair of angularly movable jaws having adjustable contact pads thereon for engaging said airfoil sectiono'n opposite sides thereof, an abutment carrying said jaws and lying on the axis of symmetry between them for engaging the trailing edge of the section, manually operable means for moving said jaws simultaneously towards and away from said axis, a frame carrying said abutment and manually operable means, a datum surface on said frame having a fixed angular relationship with said axis of symmetry and means for securing said contact pads at any predetermined distance from said abutment along said jaws.

6. A gauge for determining the direction of the zero-lift line of an airfoil section with respect to the profile thereof comprising a pair of angularly movable jaws having adjustable contact pads thereon for engaging said airfoil section on 0pposite sides thereof, an abutment carrying said jaws mounted to slide along the axis of symmetry between said jaws and having a V notch to engage the trailing edge of the section, a frame in which said abutment is slidably mounted, a pair of links angularly adjustable on the frame symmetrically about said axis and pivoted to the ends of said jaws, manually operable means for adjusting said abutment with respect to the frame to cause said jaws to move simultaneously towards and away from said axis, a datum surface on said frame having a fixed angular relationship with said axis and means for securing said contact pads at any predetermined distance from said abutment along said jaws.

7. A gauge for determining the direction of the zero-lift line of an airfoil section with re spect to the profile thereof comprising a frame, a pair of jaws pivoted on said frame and having adjustable contact pads thereon for engaging said airfoil section on opposite sides thereof, an abutment secured to said frame and having a V notch therein lying on the axis of symmetry between said jaws, a cross-head slidably mounted in said frame and engaging said jaws, means for adjusting the position of said cross-head to cause the jaws to move towards and away from said axis, a datum surface on said frame having a fixed angular relationship with said axis and means for securing said contact pads at any predetermined distance from said abutment along said jaws.

8. A gauge for determining the direction of the zero-lift line of an airfoil section with respect to the profile thereof, comprising a body having two adjustable contact members for engaging the section on opposite sides thereof, a third contact member forengaging the trailing edge of the section, and a surface on said body which bears a fixed angular relationship with a line joining said third contact, to a point midway between said two contact members, when said members engage said section at th ends of the ordinate at the mid point of the chord thereof.

HARRY LAWLEY MILNER. 

